Alkynyl-Protected Ag12Cu4 Cluster with Aggregation-Induced Emission Enhancement

Photoluminescence (PL) of atomically precise metal clusters is attractive for various applications, including light emission, chemical sensing, and bioimaging. Herein, we report the synthesis and total structure of an alkynyl-protected bimetallic AgCu cluster, Ag12Cu4(C≡CR)14(PPh3)4 (Ag12Cu4: HC≡CR = 3,5-bis(trifluoromethyl)phenylacetylene; PPh3 = triphenylphosphine), which exhibits crystallization-induced emission enhancement and aggregation-induced emission enhancement phenomena. As revealed by the single crystal X-ray diffraction data, the Ag12Cu4 cluster comprises an octahedron Ag6 core, which is stabilized by two large Ag3Cu2(C≡CR)7(PPh3)2 metal–ligand motifs. The free valence electron count suggests that Ag12Cu4 is a two-electron superatom. Interestingly, the weak PL of Ag12Cu4 solution at ≈730 nm (near-infrared region) is found to be significantly enhanced in the solid state (15 and 8 fold respectively, for the crystalline and aggregated forms). A detailed structural analysis of the Ag12Cu4 cluster reveals the presence of abundant intercluster C–H···F interactions, which significantly restrict the intramolecular rotations and vibrations, leading to strong PL enhancement in the solid state. This work will trigger the studies of other alloy metal nanoclusters with promising photophysical properties for optoelectronic and other applications.